MY 1979 CB750 DOHC BUILD

[kevint]

Do you still have those piston rings?  I am rebuilding my '79 CB750K.

Thanks

[Lucky 1]

Those frames were NOT MIG weld.
It was not available at that time.

They were stick welded.
That is why there is some spatter.

[Lucky 1]

The dimple actually shows that it is ISO threads and not JIS.


CHANGE OF THREADED PARTS
Honda Service Letter #74 6/8/67
 
In an effort to obtain more universal uniformity of threaded parts, the JIS (Japan Industrial Standards)
threaded parts standards have been modified to conform to those established by ISO (International
Standards Organization). All Japanese industry, including Honda Motor Co., is cooperating in this
change. Although the modifications of the present JIS system are not extensive, this change will require
some new tools, different tool applications, and will introduce the possibility of non-interchangeability
of similar parts.


When this went into effect it was because many motorcycles were catching fire when carb screws were interchanged. On the Honda motorcycles you will only see the dimple on the carb screws.
It was to alert the owner that they were the new ISO screws and to not put in the older JIS screws or fuel could leak from the carbs. I was a Honda dealer mechanic at that time.

[shinyribs]

Mig welding came about long before and 4 cylinder Honda's were probably even thought of. Especially a dohc.  It was invented in the 30's or early 40's to be used in aluminum welding processes but the bigger industries saw the huge potential for time savings it would provide.

[RodneyCB750K1979]

Update as of March 27 2013. I was lucky to find a good set of 4-into-4 exhaust pipes. I had to do a minor weld on a small hole in one of the collector pipes.  Visited a large cycle yard in Boise with several DOHC bikes. Picked up some extra chrome chain guards, foot pegs. Had to leave a couple sets of great looking front and rear fenders and some nice ignition coils.  All my gaskets and seals arrived so I can continue opening the engine case and replacing the seals. I cleaned, primed, and undercoated my front and rear fenders.

[RodneyCB750K1979]

Continuing with the restoration work on my 1979 CB750 L.   Received the oil seal kit for the engine. I was able to separate the crankcase but couldn't completely separate due to the generator rotor.  I tried several means of removing the rotor including use of a gear puller and the rear axle bolt but to no avail. I ordered a rotor pulling tool (bolt). If someone has a better suggestion, I would appreciate it. I started cleaning the fork bearings and ended up damaging the upper bearing seal.  Ordered a new bearing and seal. The upper bearing appears to be pressed on. I'll have to take the yoke to a machine shop to remove the old bearing inner race. Spent the last few days detail cleaning the two wheels, chain guard, struts, and wiring harness. I painted the remaining small steel pieces.  

Crankcase Lower Bolts


Crankcase Separated


Attempt at removing rotor using rear axle bolt


Wheels prepped for painting


Front fork bearing tube


Front struts with clear coating removed

[Hoosier Daddy]

Yeah, removing the inner race from the triple pivot can be a real bitch... you got a Dremel? it makes it much easier to use it with a cut-off wheel and split the race almost all the way through and then whack it with a hammer /cold chisel in the cut line.
Bits are looking mighty fine!

[TOOLS1]

I just use a cold chisel as a punch, and drive the races/bearings off the stem.
TOOLS

[RodneyCB750K1979]

Thanks for the advice.  I'll heat it with a propane torch and try driving it off.  Another example of thinking a part would come off easily and turning into a big fiasco.  This project is full of land mines.

[TOOLS1]

You should not need any heat. Maybe just an extra set of hands to hold the triple tree while you pound away.
TOOLS

[shinyribs]

I used one of these at a buddy's shop the other week.

http://www.motosport.com/dirtbike/PARK-TOOL-STEERING-RACE-REMOVER

Worked fantastically well! It'd be simple to make with a piece of good steel tubing from a hardware store.

[RodneyCB750K1979]

I got the upper bearing inner race off after some heavy strikes with a chisel and heat. Thanks for the help. Saved me some money.

[SoonerRon]

I rebuilt my 79 K engine lasf year from the bottom up. My 15 year old son helped me wrestle the engine out and later back in.  Reinstalling the engine was a pain until I figured out you need to raise the rear of the engine higher than normal to clear all the frame brackets. I had a jack in place to support the engine once we had the left side resting on the left frame rail. I wrapped cardboard around the frame to protect it while the engine was resting on it. Use the jack to adjust the height/alignment until you get the through bolts inserted. Don't forget to install the steel chain guard that bolts to the case around the front sprocket. One of the rear engine bolts must pass through it.

[RodneyCB750K1979]

I installed the engine myself using my motorcycle lift. Took a bit of shimming and adjusting the motor position but it went in.  The only casualty was my right middle finger. The motor started falling over and I reached to grab it and got my finger caught between the cam cover and the hoist frame.  Ouch.  

[RodneyCB750K1979]

Repainted the Comstar Wheels.  

[RodneyCB750K1979]

Installed the carburetors and air box. I give up. No matter what I do the images are posted upsidedown.

[csbanta]

this is an awesome documentation to follow. I am beyond envious of your knowledge

[Butcherblock]

Love those newly painted wheels. Man they look sharp. Very nice jobs on those!

[shinyribs]

Those wheels do look nice. You did a great job on them bud!

[RodneyCB750K1979]

Fired the engine up last night. Sounded great and had no problem firing. I had a fuel leak somewhere between carb 3 and 4. Probably an 0-ring on a connecting pipe.  Then I noticed some oil dripping on the floor. Traced it to loose fittings on the cylinder head oil supply tube. I had failed to tighten these during reassembly. Will tune and sync the carbs next as well as check the ignition timing.